There are many computing applications that may benefit from the use of fast nonvolatile memory. These include disk caches, solid-state drives, hard disk emulation, hybrid drives, and file systems.
For example, popular PC file systems based on FAT (File Allocation Tables) and NTFS (New Technology File System) have frequently-written file management data associated with the storage of the files. This is called “metadata”—the data that manages the file system. For a FAT32 and FAT16 based file system this is termed “FAT”, for a NTFS file system this is called MFT (Master File Table).
Accurate metadata is essential to the operation of the file system. File systems might save their metadata on one or multiple (for redundancy) disk files. However, the importance of the metadata, the frequency of metadata access and alteration, and the need for speed when accessing or altering metadata, make metadata well suited for storage in a nonvolatile RAM instead of slower disk files (or wear-sensitive NAND Flash devices), and/or as a disk cache for file system operations.
A traditional block or page accessed nonvolatile RAM such as a limited endurance (Erase Write cycling) Multi Level Cell (MLC) NAND flash device may be used to store frequently accessed data. However, directly reading and writing a NAND flash device for applications involving frequent memory operations may prove slow and cumbersome, due to the non-RAM (e.g. block-sequential) access methods typically associated with such devices. The frequently-altered nature of data in such applications may cause premature memory system failure because NAND flash devices have limited erase/write capabilities before they may wear out and become unreliable. This may result in unreliable system operation and may ultimately necessitate the replacement of the NAND flash. More frequent NAND flash replacement may greatly increase the life-cycle cost of the system.